Printed circuit boards (PCB) are used in the electronic arts as substrates to mount electronic components and to provide electrical interconnections between those components and components external to the PCB. Printed circuit boards are commonly fabricated from substrates consisting of fiber selected plastic lamina. The circuit board lamina may have one or more fiber layers surrounded by a plastic matrix material. A circuit board may have one or more laminae depending on the specific configuration needed for the electrical components. Each circuit board lamina may have a metalized pattern on one or both sides, such that, when stacked, processed, and assembled with electrical components, the metalized patterns form electrical interconnects between components.
One problem with conventional printed circuit boards is flexing. PCBs flex under the weight of attached electrical components when subject to vibrations, assembly, and handling loads. Ultimately, the PCB with attached electrical components are assembled in a chassis, such as in a computer system. Handling and transit of the chassis assembly can cause PCB flexing under the weight of the components.
Circuit boards, though relatively rigid for their relatively thin profile, tend to flex due to the weight of the circuit components attached and to shock and vibration loads. In order to support the PBC and minimize flexing, support structures attached to the PCB are commonly used. Such attachments include reinforcing bars, beams and rib stiffeners, among others. Such circuit board support or rigidifying structures are undesirable for many reasons. For example, among others, support beams may be attached to the PCB and span the entire width or length of the PCB. Such support beams take up valuable circuit board surface area, which may require offsetting or relocating some of the electrical components. This is undesirable in light of the trend to increase electrical component density on the PCB.
Additionally, electrical components are becoming increasingly heavy. Electrical components that are increasing in weight include, among others, the heatsink and fan assembly which is attached to the central processing unit (CPU). These assemblies are approaching upwards of a pound or more in weight, putting an increased burden on the structure of the PCB.
In an effort to increase electrical component density on the PCB, electrical components may be attached to the PCB using surface mount technology (SMT), such as with ball grid array (BGA) technology. A ball grid array microprocessor, for example, makes its electrical connection via a solder ball on each connector of the BGA of the electrical microprocessor and the electrical contacts on the surface of the PCB. BGA components require a rigid substrate to which they are attached. In effect, BGA components are soldered directly to the circuit board without intervening contacts or wires. BGA components commonly incorporate tens or hundreds of solder connections between the ball-grid package and the circuit board. Any appreciable circuit board flexing may cause the solder connections to shear, compress, fatigue, and subsequently break.
There is a significant need in the art to provide a PCB which is sufficiently rigid in order to support relatively heavy electrical components as well as to provide a rigid structure required for surface mount components, such as ball grid array packages.